1. Technical Field
The present invention relates to a continuously variable transmission control system for a vehicle having a continuously variable transmission device having a belt suspended between two pulleys and an electricity-driven actuator, and a control device that controls driving of the electricity-driven actuator, and to a work vehicle.
2. Related Art
In the related art, a structure is known in which a belt type continuously variable transmission device is incorporated in a motive power transmitting mechanism that transmits a motive power of a motive power source of a vehicle to a wheel. In the belt type continuously variable transmission device, a belt is suspended between a drive pulley on the side of the motive power source in the motive power transmission direction and a driven pulley on the side of the wheel. Of the drive pulley and the driven pulley, at least one pulley includes a fixed sheave and a moveable sheave which is moveable in an axial direction with respect to the fixed sheave. As the belt type continuously variable transmission device, there are known a hydraulic structure in which the moveable sheave is hydraulically moved, a mechanical structure in which the moveable sheave is moved by a pressurization force generation mechanism including a torque cam, and an electrically-driven structure in which the moveable sheave is moved by an electricity-driven actuator, and also, a combination of these structures.
JP H9-329232 A discloses an electricity-driven continuously variable transmission device which includes a cam member connected to a transmission lever, an electric motor which assists an operation force of the transmission lever, and a controller for controlling the electric motor.
JP 2005-36855 A discloses a belt type continuously variable transmission device of a combination type of electric and hydraulic structures and using a ball screw-type actuator.
JP 2003-74446 A discloses an engine startup system for motorcycles having a centrifugal clutch including a drive unit which is connected to a crank shaft of an engine and a driven unit which is connected to the drive unit at a predetermined rotational speed or greater of the drive unit, and a belt type continuously variable transmission device having a drive pulley connected to the driven unit.
As a first problem, when the moveable sheave is to be moved with a mechanical structure including a torque cam in the belt type continuously variable transmission device incorporated into a vehicle, in order to allow switching among a plurality of speed relationships which are relationships of rotational speeds of the drive pulley and the driven pulley, it is necessary to allow switching with a plurality of types of torque cam mechanisms. In this case, the structure becomes complex, and the cost may be increased.
As a second problem, in a vehicle in which the belt type continuously variable transmission device is incorporated, when a brake pedal is operated to command braking after an acceleration pedal is set to a non-operation state, a deviation may occur between the rotational speed of the driven pulley on the side of the wheel and the rotational speed of the drive pulley on the side of the motive power source. In this case, in a structure in which the centrifugal clutch is provided between the motive power source and the drive pulley, due to the cutting of the motive power transmission by the centrifugal clutch, friction between each sheave of the drive pulley and the belt may be reduced and wearing of the belt may be reduced. However, such a configuration requires the centrifugal clutch, which may cause an increase in the number of components and an increase in the manufacturing cost.
At least one advantage of the present invention is in the provision of a continuously variable transmission control system for a vehicle and a work vehicle which can switch among a plurality of speed relationships with regard to the rotational speeds of the drive pulley and the driven pulley, without requiring the switching structure of a plurality of torque cam mechanisms.
At least another advantage of the present invention is in the provision of a continuously variable transmission control system for a vehicle which can reduce wearing of the belt without requiring the centrifugal clutch.